1. Field of the Invention
The present invention relates to a scroll type fluid apparatus, such as an unlubricated scroll vacuum pump or an unlubricated scroll compressor.
2. Description of the Prior Art
Generally, a scroll type fluid apparatus comprises a casing, a fixed scroll member consisting of a mirror-finished plate fixed to the casing and a stationary lapping scroll standing upright on the plate, a drive shaft journalled on the casing and provided at its inner end, namely, one end located within the casing, with a crank, an orbiting scroll member consisting of a mirror-finished plate and a revolving scroll wrap formed so as to form a sealed space in combination with the stationary scroll wrap, and rotatably journalled on the crank of the drive shaft, and a restraining mechanism for restraining the orbiting scroll member from rotating about its own axis. When the scroll type fluid apparatus functions as an air compressor, air is sucked through a suction port formed near the outer end of the stationary scroll wrap into the compression chamber, i.e., the sealed space, the volume of the compression chamber is decreased gradually as the scroll member orbits to compress the air sucked into the compression chamber, and then the compressed air is discharged to the outside through a discharge port formed near the inner end of the stationary scroll wrap.
The orbiting scroll member must be restrained from rotating about its own axis to enable the orbiting scroll member to decrease the volume of the compression chamber formed between the stationary scroll wrap and the orbiting scroll wrap. The Oldham coupling is a well-known mechanism applicable for such a purpose. The Oldham coupling as applied to a scroll air compressor comprises an Oldham ring provided with an Oldham key seated in a keyway formed in the casing, and an Oldham key seated in a keyway formed in the reverse side of the plate of the orbiting scroll member.
When compressing air in a scroll air compressor provided with an Oldham coupling by moving the orbiting scroll member relative to the stationary scroll member, the air compressed in the compression chamber applies an axial load biasing the orbiting scroll member away from the stationary scroll member, namely, a thrust, to the orbiting scroll member, pressing the orbiting scroll member into close proximity with the Oldham coupling. Accordingly, the sliding surfaces of the orbiting scroll member and the casing engaging those of the Oldham coupling must be lubricated with a lubricating oil to ensure smooth movement of the orbiting scroll member and to prevent an abrasion of the associated parts.
On the other hand, when air is sucked into the compression chamber by the way of the orbiting scroll member, the air prevailing within the casing is sucked through minute gaps between the stationary scroll member and the orbiting scroll member into the compression chamber because a negative pressure is created within the compression chamber, entailing the flow of the mist of the lubricating oil together with the air into the compression chamber, so that the compressed air discharged by the scroll air compressor contains the lubricating oil.
Thus, the conventional scroll type fluid apparatus provided with an Oldham coupling requires the lubrication of the working surfaces of the component parts in sliding engagement, such as the Oldham coupling, the arbiting scroll member and the side wall of the casing, and needs an oil separator or the like to separate the lubricating oil from the compressed air before discharging the same, which makes the structure of the scroll type fluid apparatus complicated and increases the weight of the same.
Another known scroll type fluid apparatus employs a restraining mechanism employing an auxiliary crank disposed between the casing and the revolving scroll member and held onto the casing in a cantilever fashion. However, it is difficult for this scroll type fluid apparatus to secure a smooth revolving motion of the orbiting scroll member.